The invention relates generally to heat exchangers and more particularly to solar heat absorber units for heating by solar heat energy a fluid circulated through the units.
Diverse structures have been proposed and used in the past for the purpose of heating a fluid, preferably a liquid fluid such as water, by way of exposure of the structure to sun rays while the liquid is circulated through the structure from an inlet manifold or header to an outlet manifold or header, the liquid being progressively heated in the course of its flow progression from one header to the other. Examples of prior art methods and apparatus are disclosed in U.S. Pat. Nos. 679,451, 1,250,260, 2,358,476, 2,553,302, 3,076,450, 3,077,190, 3,145,707, 3,190,816, 3,387,602, 3,239,000, 3,273,227, 3,980,071, and Australian Patent specifications Nos. 53,407 and 257,425.
Many inconveniences are present in prior art devices, which are due to many reasons, such as the type of materials used for making the solar heat absorber unit, the small volume of liquid flowing through the unit, the complication of many designs, the difficulty of manufacturing and the resultant high cost of production, to name a few. Solar energy absorbers most practical under the present state of the art, as far as relative simplicity of structure and relatively low cost, seem to belong generally to two types. The first type takes the form of a plurality of parallel, spaced apart metallic tubes interconnecting an inlet header to an outlet header, soldered or welded to a heat absorbing flat or corrugated panel made of thin metallic sheet or foil. The second type of solar energy absorber panels generally used today are based on a structure, as disclosed in U.S. Pat. No. 3,273,227, made of a pair of superimposed metallic sheets provided at their adjoining areas with a pattern of weld inhibiting material coating, welded together at the areas not provided with the welding inhibiting material, and subsequently inflated under pressure along the unwelded areas to form interconnecting tubular portions. Such structures have in common the disadvantage that the area of the absorber panel through which the liquid is caused to flow, or wetted area, is a relatively small portion of the total area of the panel, with the result that the efficiency, or BTU capability per area unit of such panels, is relatively poor.